Light-emitting chip and device using the same

ABSTRACT

A light-emitting chip includes a light-emitting unit, first and second electrode units. The light-emitting unit includes first and second conductivity type semiconductor layers and an active layer. The first electrode unit includes two first electrodes which are spaced apart from each other by a first distance, and which are electrically connected to the first conductivity type semiconductor layer. The second electrode unit includes two second electrodes electrically connected to the second conductivity type semiconductor layer. The first and second electrode units are spaced apart from each other by a second distance, and the first distance is greater than the second distance.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Chinese Invention Patent ApplicationNo. 202110007123.8, filed on Jan. 5, 2021, and Chinese Invention PatentApplication No. 202110500339.8, filed on May 8, 2021.

FIELD

The disclosure relates to a light-emitting diode (LED), and moreparticularly to a light-emitting chip and a light-emitting deviceincluding the same. The disclosure also relates to an optical-projectingdevice.

BACKGROUND

In some applications, light-emitting chips are required to have a highcurrent density. For example, each of the light-emitting chip in themicro projector currently on market may include a blue/green channelthat requires a current density of 5 A/mm² to 6 A/mm², and a red channelthat requires a current density of 4 A/mm² to 5 A/mm². In addition,certain light-emitting products may have two 2.0 mm² ultra-verticalchips electrically connected in parallel to obtain a 4.0 mm²light-emitting surface in the blue channel, and the driving currentrequired for the ultra-vertical chips can reach as high as 20 A.

The driving current of a 2.0 mm² horizontal and vertical chip may be 10A at 5 A/mm², and may even reach 12 A at 6 A/mm². In consideration ofthe fact that the driving current continues to increase, and thatselection of a power supply for the product (e.g., a light-emittingchip) becomes more stringent, a horizontal and vertical chip structurehave been introduced into the market to be made into a tandemhigh-voltage low-current light source.

With continued increase of current density, the need for chip currentdistribution and thermal management of chip package have also increased.The use of insulating substrates in horizontal and vertical chips canachieve wafer-level thermoelectric separation. In addition of optimizingvia configuration (e.g., blue/green channel(s)) and extension barconfiguration (e.g., red channel(s) of a P side up light-emitting chip),electrode distribution also has a significant impact on currentdistribution. In a product with a high current density demand and/orbeing made of semiconductor materials with a low carrier mobility,optimization of electrode distribution in a light-emitting chip isrequired in order to improve current distribution.

Referring to FIGS. 1 and 2, a conventional light-emitting chip 1 isprovided. FIG. 2 is a perspective front view of the conventionallight-emitting chip 1 shown in FIG. 1. The conventional light-emittingchip 1 includes an N-type electrode 11 and a P-type electrode 12 (i.e.,an electrode layout of 1P1N). The conventional light-emitting chipfurther includes a semiconductor stack 13 containing a firstconductivity type semiconductor layer 131 (N-type), a secondconductivity type semiconductor layer (P-type) 132, and a photoelectricactive layer 133 disposed between the first conductivity typesemiconductor layer 131 and the second conductivity type semiconductorlayer 132.

The N-type electrode 11 is electrically connected to the firstconductivity type semiconductor layer 131 through a first electricalconnection layer 14. The first electrical connection layer 14 contactsat least a part of a bottom portion of the first conductivity typesemiconductor layer 131, and is disposed between the first conductivitytype semiconductor layer 131 and a permanent substrate 10.

The first electrical connection layer 14 has an exposed portion that isexposed from the first conductivity type semiconductor layer 131 andthat forms a first platform 141. The N-type electrode 11 is formed onthe exposed portion (i.e., first platform 141) of the first electricalconnection layer 14. The first platform 141 provides an electricalconnection (e.g., N-type electrical connection) between the N-typeelectrode 11 and the first conductivity type semiconductor layer 131.

In some wafer manufacturing processes, the first conductivity typesemiconductor layer 131, the second conductivity type semiconductorlayer 132, and the photoelectric active layer 133 of the semiconductorstack 13 are sequentially grown by vapor deposition on a growthsubstrate (not shown), and then the growth substrate is peeled off fromthe semiconductor stack 13, followed by forming the first electricalconnection layer 14 on the first conductivity type semiconductor layer131. The first electrical connection layer 14 is then connected to thepermanent substrate 10.

A second electrical connection layer 15 might be disposed between theP-type electrode 12 and the second conductivity type semiconductor layer132. The second electrical connection layer 15 functions as a secondplatform 141 for supporting the P-type electrode 12, and provideselectrical connection between the P-type electrode 12 and the secondconductivity type semiconductor layer 132. The second electricalconnection layer 15 might include a metal layer, a transparent currentspread layer, or a doped semiconductor layer. The P-type electrode 12and the first electrical connection layer 14 are respectively arrangedon opposite sides of the semiconductor stack 13. An electric current isvertically injected from the P-type electrode 12 into the semiconductorstack 13, and flows from the semiconductor stack 13 to the firstelectrical connection layer 14. The arrows shown in FIG. 2 indicateschematically a direction of the electric current flowing through theconventional light-emitting chip 1. Since the P-type electrode 12 has ahigh current density, it is likely to cause local heat accumulation andbrightness reduction problems in the conventional light-emitting chip 1.

SUMMARY

Therefore, an object of the disclosure is to provide a light-emittingchip, a light-emitting device, and an optical-projecting device that canalleviate at least one of the drawbacks of the prior art. In thisdisclosure, the light-emitting chip is provided with an improved currentspread, reduced heat accumulation, and improved brightness.

According to a first aspect of the present disclosure, thelight-emitting chip includes a light-emitting unit, a first electrodeunit, and a second electrode unit. The light-emitting unit includes afirst conductivity type semiconductor layer, an active layer, and asecond conductivity type semiconductor layer sequentially arranged alonga first direction. The first electrode unit includes two firstelectrodes which are spaced apart from each other by a first distance,and which are electrically connected to the first conductivity typesemiconductor layer. The second electrode unit includes two secondelectrodes which are electrically connected to the second conductivitytype semiconductor layer. The first electrode unit and the secondelectrode unit are spaced apart from each other by a second distance,and the first distance is greater than the second distance.

According to a second aspect of the present disclosure, thelight-emitting device includes at least one of the aforesaidlight-emitting chip and a circuit board electrically connected to thelight-emitting chip.

According to a third aspect of the present disclosure, theoptical-projecting device includes at least one of the aforesaidlight-emitting chip, a support for holding the light-emitting chip, anda power supply for supplying power to the light-emitting chip.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the disclosure will become apparent inthe following detailed description of the embodiments with reference tothe accompanying drawings, of which:

FIG. 1 is a schematic top view of a conventional light-emitting chipwith a P-type electrode and an N-type electrode;

FIG. 2 is a perspective front view of the conventional light-emittingchip;

FIG. 3 is a schematic top view of a first embodiment of a light-emittingchip having two P-type electrodes and two N-type electrodes according tothe present disclosure;

FIG. 4 is a perspective cross-sectional view along line A-B of the firstembodiment of the light-emitting chip shown in FIG. 3;

FIG. 5 is a perspective cross-sectional view of a second embodiment ofthe light-emitting chip according to the present disclosure;

FIG. 6 is a plot showing forward voltages of the conventionallight-emitting chip and the second embodiment of the light-emitting chipof the present disclosure at different current densities;

FIG. 7 is a plot showing output power of the conventional light-emittingchip and the second embodiment of the light-emitting chip of the presentdisclosure at different current densities;

FIG. 8 is a plot showing peak wavelengths of the conventionallight-emitting chip and the second embodiment of the light-emitting chipof the present disclosure at different current densities;

FIG. 9 is a plot showing main wavelengths (WLD) of the conventionallight-emitting chip and a third embodiment of the light-emitting chip ofthe present disclosure at different current densities;

FIGS. 10 and 11 are schematic top views of a fourth embodiment of thelight-emitting chip according to the present disclosure;

FIG. 12 is a schematic top view of a fifth embodiment of thelight-emitting chip according to the present disclosure; and

FIG. 13 is a schematic top view of a sixth embodiment of thelight-emitting chip according to the present disclosure.

DETAILED DESCRIPTION

Before the disclosure is described in greater detail, it should be notedthat where considered appropriate, reference numerals or terminalportions of reference numerals have been repeated among the figures toindicate corresponding or analogous elements, which may optionally havesimilar characteristics.

Referring to FIGS. 3 and 4, a first embodiment of a light-emitting chip2 according to the present disclosure is provided. FIG. 4 is across-sectional view along line A-B of the light-emitting chip 2 shownin FIG. 3. The light-emitting chip 2 includes an electrically insulatingsubstrate 20, a first electrode unit 21, a second electrode unit 22, anda light-emitting unit 23. The first electrode unit 21, the secondelectrode unit 22, and the light-emitting unit 23 are disposed on theelectrically insulating substrate 20. The light-emitting unit 23includes a first conductivity type semiconductor layer 231, an activelayer 233, and a second conductivity type semiconductor layer 232sequentially arranged along a first direction. The first electrode unit21 includes two first electrodes 211 which are spaced apart from eachother by a first distance (D1) and which are electrically connected tothe first conductivity type semiconductor layer 231. In someembodiments, the first conductivity type semiconductor layer 231 is anN-type semiconductor layer, and the first electrodes 211 are N-typeelectrodes. The second electrode unit 22 includes two second electrodes221 which are electrically connected to the second conductivity typesemiconductor layer 232. In some embodiments, the second conductivitytype semiconductor layer 232 is a P-type semiconductor layer, and thesecond electrodes 221 are P-type electrodes. In this embodiment, thefirst electrode unit 21 and the second electrode unit 22 are spacedapart from each other by a second distance (D2), and the first distance(D1) is greater than the second distance (D2). Each of the firstelectrodes 211 and the second electrodes 221 has a projection on asurface of the electrically insulating substrate 20. The second distance(D2) is a minimum distance between the projection of one of the firstelectrodes 211 and the projection of a corresponding one of the secondelectrodes 221 that is relatively close to the one of the firstelectrodes 211. The two first electrodes 211 are spaced apart from thelight-emitting unit 23 and respectively disposed at opposite sides ofthe light-emitting unit 23. The two second electrodes 221 arerespectively disposed on the light-emitting unit 23 at opposite sides ofthe light-emitting unit 23.

In some embodiments, the first electrode unit 21 may have a plurality ofpairs of the first electrodes 211, and the second electrode unit 22 mayhave a plurality of pairs of the second electrodes 221. In certainembodiments, the light-emitting chip 2 includes 2n of the firstelectrode unit 21, n being a positive integer. In certain embodiments,the light-emitting chip 2 includes 2m of the second electrode unit 22, mbeing a positive integer.

In some embodiments, each of the first electrodes 211 and the secondelectrodes 221 has a rectangular cross-section perpendicular to thefirst direction. The rectangular cross-section has a long side and ashort side. In certain embodiments, the long side has a length that isabout 4 times to about 8 times a length of the short side, which isconvenient for multiple wires to bond to a single electrode since thegreater the length of the long side of the electrodes (i.e., the firstelectrodes 211 and the second electrodes 221), the larger the areaavailable for connecting the wires. In certain embodiments, the lengthof the short side ranges from about 30 μm to about 80 μm.

In some embodiments, the light-emitting chip 2 may further include afirst electrical interconnection layer 24 and a second electricalinterconnection layer 25. The first electrical interconnection layer 24electrically connects the first electrodes 211 of the first electrodeunit 21 to the first conductivity type semiconductor layer 231. Thesecond electrical interconnection layer 25 electrically connects thesecond electrodes 221 of the second electrode unit 22 to the secondconductivity type semiconductor layer 232. The first electricalinterconnection layer 24 may be disposed under the first conductivitytype semiconductor layer 231 and may have an exposed portion exposedfrom the first conductivity type semiconductor layer 231. The exposedportion functions as a first platform 241 on which the first electrodes211 are disposed. The second electrical interconnection layer 25 isformed with a second platform 251 to support the second electrodes 221(i.e., the second electrodes 221 of the second electrode unit 22 aredisposed on the second electrical interconnection layer 25). In certainembodiments, the active layer 233 may be disposed between the firstelectrical interconnection layer 231 and the second electrode unit 22.In some embodiments, each of the second electrodes 221 has a firstsurface 2211 and a second surface 2212 opposite to the first surface2211. The first surface 2211 of each of the second electrodes 221 facestoward the active layer 233, and the second surface 2212 of each of thesecond electrodes 221 faces toward the first direction (i.e., facing adirection away from the active layer 233). Each of the first electrodes211 has a first surface 2111 and a second surface 2112 opposite to thefirst surface 2111. The first surface 2111 of each of the firstelectrodes 211 faces toward the first electrical interconnection layer24, and the second surface 2112 of each of the first electrodes 211faces toward the first direction (i.e., faces a direction away from thefirst electrical interconnection layer 24). In other words, in thisembodiment, the light-emitting chip 2 is a lateral light-emitting chip.

In some chip manufacturing processes, semiconductor layers (i.e., thefirst conductivity type semiconductor layer 231, the active layer 233,and the second conductivity type semiconductor layer 232) are sequentialgrown on a temporary substrate (not shown) by vapor deposition, and thenthe temporary substrate are separated from the semiconductor layers bylaser or etching techniques. The first electrical interconnection layer24 is then formed on the first conductivity type semiconductor layer231, and the first electrical interconnection layer 24 is bonded to theelectrically insulating substrate 20. In this embodiment, the firstelectrical interconnection layer 24 is disposed between the electricallyinsulating substrate 20 and the first conductivity type semiconductorlayer 231. In certain embodiments, the light-emitting chip 2 has an areathat ranges from about 1 mm² to about 3 mm². To be specific, theelectrically insulating substrate 20 of the light-emitting chip 2 has asurface 234 distal from the first electrical interconnection layer 24.The surface 234 has an area that ranges from about 1 mm² to about 3 mm².

The arrows shown in FIG. 4 indicate schematically a direction ofelectric current paths which are optimized in the light-emitting chip 2.The electric current flows from the second electrodes 221 into thelight-emitting chip 2. When the lateral current spreading ability of thelight-emitting unit 23 is low, the current tends to concentrate mainlyunder the second electrodes 221. Therefore, in some embodiments, thefirst distance (D1) is at least 10 times greater than the seconddistance (D2) so as to control current distribution in thelight-emitting chip 2. In this embodiment, the light-emitting chip has arectangular cross-section that is perpendicular to the first directionand that has a long side and a short side. In some embodiments, thefirst distance (D1) is greater than about 50% of a length of the longside of the rectangular cross-section of the light-emitting chip 2. Thefirst electrodes 211 and the second electrodes 221 may be made of atleast one of a material including, but not limited to, gold, tin,platinum, titanium, chromium, aluminum, and nickel.

The light-emitting chip 2 may have great reliability under a highcurrent. In some embodiments, the light-emitting chip 2 may be operatedunder a current higher than 8 A, and have a current density of greaterthan about 3 A/mm².

In high-current applications, the second electrodes 221 of thisembodiment are disposed as far away as possible from each other on thesecond platform 251. By combining the aforesaid design of the secondelectrodes 221 with the design of the first electrodes 211 according tothe present disclosure, the current can be laterally distributed on thesecond platform 251 to reduce current accumulation, which improvesphotoelectric performance of a product using the light-emitting chip 2of the present disclosure.

Referring to FIG. 5, a second embodiment of the light-emitting chip 2according to the present disclosure is provided. The second embodimentof the light-emitting chip 2 has a structure similar to that of thefirst embodiment, except that, in the second embodiment, thelight-emitting chip 2 is a gallium arsenide-based light-emitting chip inwhich at least one of the first conductivity type semiconductor layer231, the second conductivity type semiconductor layer 232, and theactive layer 233 is a gallium arsenide-based layer made of a galliumarsenide-based material.

In this embodiment, the gallium arsenide-based material of the at leastone the first conductivity type semiconductor layer 231, the secondconductivity type semiconductor layer 232, and the active layer 233 hasa carrier mobility (e.g., electron mobility) that is usually not greaterthan about 500 cm²/V·s. Since the carrier mobility of the galliumarsenide-based material is lower than that of gallium nitride, thelateral current spreading ability of the current in the light emittingunit 2 is relatively poor. Therefore, the second electricalinterconnection layer 25 of the second embodiment of the light-emittingchip 2 disposed between the second conductivity type semiconductor layer232 and the second electrodes 221 may be made of a metal, a transparentand electrically conductive material, or a doped semiconductor materialto improve current spreading. For example, a doped galliumphosphide-based layer with a roughened surface may be disposed betweenthe second conductivity type semiconductor layer 232 and the secondelectrodes 221 to serve as the second electrical interconnection layer25. In certain embodiments, the doped gallium phosphide-based layer hasan electron mobility of not greater than about 500 cm²/(V·s) and greaterthan that of the gallium arsenide-based material. The roughened surfaceof the doped gallium phosphide-based layer and a light-exiting surfaceof the light-emitting chip 2 face toward a same direction so that lightextraction efficiency is improved. In some embodiments, the dopedgallium phosphide-based layer has a thickness that ranges from about 2μm to about 4 μm. In certain embodiments, the doped galliumphosphide-based layer includes magnesium. In some other embodiments, thesecond electrical interconnection layer 25 may be a transparent currentspreading layer.

Referring to FIGS. 6 to 8, forward voltage, output power, and peakwavelength at different current densities are compared between theconventional light-emitting chip 1 with the 1P1N electrode layout (seeFIGS. 1 and 2) and the second embodiment of the light-emitting chip 2with the 2P2N electrode layout. The conventional light-emitting chip 1and the second embodiment of the light-emitting chip 2 used for testingin the present disclosure are both red p-side up light-emitting chips.The data show that under the same epitaxial process conditions, thesecond embodiment of the light-emitting chip (i.e., the light-emittingchip with the 2P2N electrode layout) has an improved photoelectricefficiency and a reduced forward voltage compared with the conventionallight-emitting chip 1 (i.e., the light-emitting chip with the 1P1Nelectrode layout) at a current density below 500 A/cm², that is, below 5A/mm², with each of the light-emitting chips 1, 2 having a chip area of2 mm². Compared with the conventional light-emitting chip 1, at 500A/cm², the forward voltage (V_(f)) of the second embodiment of thelight-emitting chip 2 is reduced by about 0.4 V (shown in FIG. 6), theoutput power (i.e., brightness) of the second embodiment of thelight-emitting chip 2 is increased by about 0.5 W (shown in FIG. 7), awall-plug efficiency (WPE) of the second embodiment of thelight-emitting chip 2 is increased by about 24% (can be inferred fromthe results shown in FIGS. 6 and 7), and the saturation current of thesecond embodiment of the light-emitting chip 2 has increased. Theaforesaid measured data shows that reliability of the light-emittingchip 2 operating under high current conditions has improved.

In addition, the degree of red shift of the second embodiment of thelight-emitting chip 2 is slightly different from that of theconventional light-emitting chip 1 as current density increases, whichalso suggests that the overall current distribution and heatdistribution has improved by optimization of the electrode layout, i.e.,using the 2P2N electrode layout of the present disclosure.

A third embodiment of the light-emitting chip 2 of the presentdisclosure has a structure similar to that of the second embodiment,except that in the third embodiment, the light-emitting chip 2 is agallium nitride-based light-emitting chip in which at least one of thefirst conductivity type semiconductor layer 231, the second conductivitytype semiconductor layer 232, and the active layer 233 is a galliumnitride-based layer. Referring to FIG. 9, due to the 2P2N electrodelayout of the third embodiment of the light-emitting chip 2, the currentpath in the light-emitting chip 2 is improved, and the WPE is alsoimproved compared with those of the conventional light-emitting chip 1.Since gallium arsenide has a carrier mobility lower than that of galliumnitride, the overall improvement relative to the 1P1N electrode layoutmay not be as large as that of the gallium arsenide-based light-emittingchip 2 disclosed in the second embodiment.

In order to meet the packaging requirements of a high-voltage device ora series connecting device, a fourth embodiment of the light-emittingchip 2, which is a light-emitting device including the light-emittingchip 2 of the present disclosure, is provided. The light-emitting deviceincludes a plurality of the light-emitting chips 2, and thelight-emitting chips 2 are electrically connected to each other.Referring to FIG. 10, the light-emitting chips 2 are electricallyconnected by wires 3. Each of the light-emitting chips 2 has a structurethe same as any of the first to third embodiments. Since the firstelectrodes 211 and the second electrodes 221 are located at oppositesides of the light-emitting unit 23, such design facilitates wireconnection between the light-emitting chips 2 of the light-emittingdevice, which simplifies circuit design of the light-emitting device andshortens wiring distance.

Referring to FIG. 11, as mentioned in the first embodiment, each of thefirst electrodes 211 and the second electrodes 221 of the light-emittingdevice has the rectangular cross-section, which has the long side andthe short side. In certain embodiments, the short side has a length thatranges from about 30 μm to about 80 μm. When the light-emitting deviceis applied with a high current, for example, a current greater than 3 A,multiple wires 3 are used for shunting the current.

To be specific, in this embodiment, two light-emitting chips 2 areconnected in series in the light-emitting device. In this embodiment,four wires 3 are preferably used to connect each of the electrodes(i.e., the first and second electrodes 211, 221) and the circuit board4, and the four wires 3 are designed to shunt the input current.

In some embodiments, connection between the light-emitting chips 2 ofthe light-emitting device can be altered according to the locations ofthe first and second electrodes 211, 221.

Referring to FIG. 12, a fifth embodiment of the light-emitting chip 2 ofthe present disclosure is provided. The fifth embodiment of thelight-emitting chip 2 has a structure similar to that of the firstembodiment, except that in the fifth embodiment, the first electrodes211 of the first electrode unit 21 are arranged diagonally with respectto the light-emitting unit 23, disposed at opposite sides of thelight-emitting unit 23, and are spaced apart from the light-emittingunit 23 and the second electrodes 221. The second electrodes 221 of thesecond electrode unit 22 are arranged diagonally at opposite sides ofthe light-emitting unit 23, disposed on the light-emitting unit 23, andare spaced apart from the first electrodes 211. The distance (D1)between the first electrodes 211 is greater than the distance (D2)between the one of the first electrodes 211 and the second electrode 212adjacent to the first electrode 211.

Referring to FIG. 13, a sixth embodiment of the light-emitting chip 2 ofthe present disclosure is provided. By removing a portion of thelight-emitting unit 23 to expose the first electrical interconnectionlayer 24, a plurality of the first platforms 241 (i.e., exposed portionsof the first electrical interconnection layer 24) are formed and arearranged at intervals at one side of the light-emitting unit 23. In thisembodiment, the first electrodes 211 and the second electrodes 221 arealternately arranged at one side of the light-emitting unit 23 and arespaced apart from each other. The distance (D1) between the firstelectrodes 211 is greater than the distance (D2) between one of thefirst electrodes 211 and a corresponding one of the second electrodes221 that is adjacent to the one of the first electrodes 211.

An optical-projecting device including one of the light-emitting chips 2and the light-emitting devices disclosed in the first to sixthembodiments of the present disclosure is also disclosed. To be specific,the optical-projecting device includes one of the light-emitting chips 2and the light-emitting devices disclosed in the first to sixthembodiments, a support for holding the light-emitting chip 2 and/or thelight-emitting device, and a power supply for supplying power to thelight-emitting chip 2 and/or the light-emitting device. The support maybe, but not limited to, a box or a frame structure.

The embodiments of the present disclosure have the following advantages.The light-emitting chip of the present disclosure is mainly used forproducing gallium arsenide-based epitaxial products that emits redlight, and is designed so that under a high current density, thelight-emitting chip has a reduced working voltage, an improvedbrightness, an improved photoelectric conversion efficiency, and anincreased saturation current. In addition, there is a slight differencein the degree of red shift of the light-emitting chip as current densityincreases, which also supports the fact that optimization of electrodedistribution according to the present disclosure improves overallcurrent distribution and heat distribution of the light-emitting chip.The light-emitting chip of the present disclosure may also be used forproducing gallium nitride-based epitaxial products.

In the description above, for the purposes of explanation, numerousspecific details have been set forth in order to provide a thoroughunderstanding of the embodiments. It will be apparent, however, to oneskilled in the art, that one or more other embodiments may be practicedwithout some of these specific details. It should also be appreciatedthat reference throughout this specification to “one embodiment,” “anembodiment,” an embodiment with an indication of an ordinal number andso forth means that a particular feature, structure, or characteristicmay be included in the practice of the disclosure. It should be furtherappreciated that in the description, various features are sometimesgrouped together in a single embodiment, figure, or description thereoffor the purpose of streamlining the disclosure and aiding in theunderstanding of various inventive aspects, and that one or morefeatures or specific details from one embodiment may be practicedtogether with one or more features or specific details from anotherembodiment, where appropriate, in the practice of the disclosure.

While the disclosure has been described in connection with what areconsidered the exemplary embodiments, it is understood that thisdisclosure is not limited to the disclosed embodiment(s) but is intendedto cover various arrangements included within the spirit and scope ofthe broadest interpretation so as to encompass all such modificationsand equivalent arrangements.

What is claimed is:
 1. A light-emitting chip comprising: alight-emitting unit including a first conductivity type semiconductorlayer, an active layer, and a second conductivity type semiconductorlayer sequentially arranged along a first direction; a first electrodeunit including two first electrodes which are spaced apart from eachother by a first distance, and which are electrically connected to saidfirst conductivity type semiconductor layer; and a second electrode unitincluding two second electrodes which are electrically connected to saidsecond conductivity type semiconductor layer, wherein said firstelectrode unit and said second electrode unit are spaced apart from eachother by a second distance, and said first distance is greater than saidsecond distance.
 2. The light-emitting chip as claimed in claim 1,wherein said first electrodes of said first electrode unit are spacedapart from said light-emitting unit and respectively disposed atopposite sides of said light-emitting unit.
 3. The light-emitting chipas claimed in claim 1, wherein said second electrodes of said secondelectrode unit are respectively disposed on said light-emitting unit atopposite sides of said light-emitting unit.
 4. The light-emitting chipas claimed in claim 1, further comprising a first electricalinterconnection layer and a second electrical interconnection layer,said first electrical interconnection layer electrically connecting saidfirst electrodes of said first electrode unit to said first conductivitytype semiconductor layer, said second electrical interconnection layerelectrically connecting said second electrodes of said second electrodeunit to said second conductivity type semiconductor layer, wherein saidfirst electrical interconnection layer is disposed under said firstconductivity type semiconductor layer and has an exposed portion exposedfrom said first conductivity type semiconductor layer, said firstelectrodes of said first electrode unit are disposed on said exposedportion of said first electrical interconnection layer, and said secondelectrodes of said second electrode unit are disposed on said secondconductivity type semiconductor layer.
 5. The light-emitting chip asclaimed in claim 4, wherein said active layer is disposed between saidfirst electrical interconnection layer and said second electrode unit.6. The light-emitting chip as claimed in claim 1, wherein said firstconductivity type semiconductor layer has an electron mobility of notgreater than 500 cm²/V·s.
 7. The light-emitting chip as claimed in claim1, wherein said second conductivity type semiconductor layer has anelectron mobility of not greater than 500 cm²/V·s.
 8. The light-emittingchip as claimed in claim 1, wherein at least one of said firstconductivity type semiconductor layer, said second conductivity typesemiconductor layer, and said active layer is a gallium arsenide-basedlayer.
 9. The light-emitting chip as claimed in claim 1, furthercomprising an electrical interconnection layer disposed between saidsecond conductivity type semiconductor layer and said second electrodeunit.
 10. The light-emitting chip as claimed in claim 9, wherein saidelectrical interconnection layer is a transparent current spreadinglayer.
 11. The light-emitting chip as claimed in claim 9, wherein saidelectrical interconnection layer is a doped gallium phosphide-basedlayer, said doped gallium phosphide-based layer having a roughenedsurface.
 12. The light-emitting chip as claimed in claim 11, whereinsaid doped gallium phosphide-based layer has an electron mobility of notgreater than 500 cm²/(V·s).
 13. The light-emitting chip as claimed inclaim 11, wherein said doped gallium phosphide-based layer has athickness that ranges from 2 μm to 4 μm; and said doped galliumphosphide-based layer includes magnesium.
 14. The light-emitting chip asclaimed in claim 1, further comprising an electrically insulatingsubstrate, said first electrical interconnection layer being disposedbetween said substrate and said first conductivity type semiconductorlayer.
 15. The light-emitting chip as claimed in claim 14, wherein saidelectrically insulating substrate has a surface distal from said firstelectrical interconnection layer, said surface having an area thatranges from 1 mm² to 3 mm².
 16. The light-emitting chip as claimed inclaim 1, wherein each of said second electrodes has a first surface anda second surface opposite to said first surface, said first surface ofeach of said second electrodes facing toward said active layer and saidsecond surface of each of said second electrodes facing toward saidfirst direction; and each of said first electrodes has a first surfaceand a second surface opposite to said first surface, said first surfaceof each of said first electrodes facing toward said first direction. 17.The light-emitting chip as claimed in claim 1, wherein saidlight-emitting chip has a current density of greater than 3 A/mm². 18.The light-emitting chip as claimed in claim 1, wherein said firstdistance is at least 10 times greater than said second distance.
 19. Thelight-emitting chip as claimed in claim 1, wherein: said light-emittingchip has a rectangular cross-section perpendicular to said firstdirection, said rectangular cross-section having a long side and a shortside; and said first distance is greater than 50% of a length of saidlong side of said rectangular cross-section of said light-emitting chip.20. The light-emitting chip as claimed in claim 1, wherein each of saidfirst electrodes and said second electrodes is made of a materialincluding one of gold, tin, platinum, titanium, chromium, aluminum,nickel, and combinations thereof.
 21. The light-emitting chip as claimedin claim 1, wherein: each of said first electrodes and said secondelectrodes has a rectangular cross-section perpendicular to said firstdirection, said rectangular cross-section having a long side and a shortside; and said short side has a length that ranges from 30 μm to 80 μm.22. The light-emitting chip as claimed in claim 1, wherein: each of saidfirst electrodes and said second electrodes has a rectangularcross-section perpendicular to said first direction, said rectangularcross-section having a long side and a short side; and said long sidehas a length that is 4 times to 8 times a length of said short side. 23.The light-emitting chip as claimed in claim 1, wherein: saidlight-emitting chip includes 2n of said first electrode unit, n being apositive integer; and said light-emitting chip includes 2m of saidsecond electrode unit, m being a positive integer.
 24. A light-emittingdevice comprising: at least one light-emitting chip as claimed in claim1; and a circuit board electrically connected to said light-emittingchip.
 25. The light-emitting device as claimed in claim 24, wherein saidlight-emitting device includes a plurality of said light-emitting chips,said light-emitting chips being electrically connected to each other.26. An optical-projecting device comprising: at least one light-emittingchip as claimed in claim 1; a support for holding said light-emittingchip; and a power supply for supplying power to said light-emittingchip.